function picks = nms_multiclass(boxes, overlap)
% top = nms(boxes, overlap)
% Non-maximum suppression. (FAST VERSION)
% Greedily select high-scoring detections and skip detections
% that are significantly covered by a previously selected
% detection.
%
% NOTE: This is adapted from Pedro Felzenszwalb's version (nms.m),
% but an inner loop has been eliminated to significantly speed it
% up in the case of a large number of boxes

% Copyright (C) 2011-12 by Tomasz Malisiewicz
% All rights reserved.
% 
% This file is part of the Exemplar-SVM library and is made
% available under the terms of the MIT license (see COPYING file).
% Project homepage: https://github.com/quantombone/exemplarsvm


if isempty(boxes)
  picks = {};
  return;
end

if size(boxes, 1) < 10000
    picks = nms_multiclass_mex(double(boxes), double(overlap));
    return;
end

x1 = boxes(:,1);
y1 = boxes(:,2);
x2 = boxes(:,3);
y2 = boxes(:,4);

area = (x2-x1+1) .* (y2-y1+1);

picks = cell(size(boxes, 2)-4, 1);
for iS = 5:size(boxes, 2)
    s = boxes(:,iS);
    [~, I] = sort(s);

    pick = s*0;
    counter = 1;
    while ~isempty(I)
      last = length(I);
      i = I(last);  
      pick(counter) = i;
      counter = counter + 1;

      xx1 = max(x1(i), x1(I(1:last-1)));
      yy1 = max(y1(i), y1(I(1:last-1)));
      xx2 = min(x2(i), x2(I(1:last-1)));
      yy2 = min(y2(i), y2(I(1:last-1)));

      w = max(0.0, xx2-xx1+1);
      h = max(0.0, yy2-yy1+1);

      inter = w.*h;
      o = inter ./ (area(i) + area(I(1:last-1)) - inter);

      I = I(o<=overlap);
    end

    pick = pick(1:(counter-1));
    picks{iS-4} = pick;
end
